Gas ion lasers are characterized by a gas discharge tube which includes an anode and a cathode defining an arc discharge within the tube. The arc discharge induces significant amount of heat which must be dissipated out of the bore of the gas discharge tube. A common method for controlling the temperature within the discharge tube is to provide a plurality of heat conduction structures inside the vacuum envelope of the discharge tube which consist basically of discs having an inside aperture. The inside aperture of the disc limits the gas discharge to a bore typically along the center of the tube. Heat is radiated into the heat conduction structure and out to the inside surface of the vacuum envelope. The outside surface of the vacuum envelope is cooled to remove the heat. This basic structure is described, for example, in U.S. Pat. No. 4,719,638, entitled DISCHARGE TUBE FOR A GAS LASER, by Carlson, et al., issued Jan. 12, 1988.
A variety of alternative discharge tube designs exist, many of which include heat conduction structures within the vacuum envelope of the tube. These systems are characterized by erosion of the heat conduction structure due to the sputtering effect of high energy ions from the gas discharge. In gas discharge tubes, such as described in Carlson, et al., and such as used in the Spectra-Physics Model 2040 argon ion laser, manufactured by Spectra-Physics Lasers, Inc., in Mountain View, Calif., the heat conducting structures comprise a web member, a shield member and an inside bore disc. The web member is brazed to an inside surface of a ceramic cylinder serving as the vacuum envelope of the tube and includes a number of holes which establishes a gas bypass path adjacent the inside surface of the cylinder. The shield member establishes a shield between the gas bypass path and the arc through the discharge tube. The inside bore disc is manufactured of a sputter resistant metal such as tungsten, and has an inside aperture which limits the gas discharge and defines the outside diameter of the bore.
The aperture size is designed to optimize the performance of the laser, in combination with factors like the length of the discharge tube, the power limitation, and beam quality. A small diameter aperture increases the current density within the bore and thereby laser efficiency. However, a small diameter aperture suffers very high erosion rates because of the increased concentration of higher energy ions in the discharge which increases the sputtering rate.
Therefore, it is desirable to provide a heat conduction structure which allows optimizing the design of a gas discharge tube for ion lasers, while increasing the resistance of the heat conduction structure to erosion by sputtering.